Stepwise Insertion of Alkylisocyanides into the Metal-Alkyne Bond of Half-Sandwich Type Rhodium Complexes: Synthesis and Structural Characterization of Metallacyclobutenes and Metallacyclopentenes

The cyclopentadienyl complexes [C5H5Rh(RCCR′)(SbiPr3)] (5–8), which were prepared from trans‐[RhCl‐(RCCR′)(SbiPr3)2] (1–4) and NaC5H5 and which contain a labile Rh–SbiPr3 bond, reacted with CO and CNR″ (R″ = Me, tBu) to give the carbonyl and isocyanide derivatives [C5H5Rh(RCCR′)(CO)] (9–11) and [C5H5Rh(RCCR′)‐(CNR″)] (12–16), respectively. On treatment of 12 (R = R′ = Ph; R″ = Me) with SbiPr3, the metallacyclobutene complex [C5H5Rh{κ2(C,C}‐C( = NMe)CPh=CPh}(SbiPr3)] (17) was formed; it reacts with excess CNMe or CNtBu to yield the metallacyclopentenes [C5H5Rh{κ2(C,C)‐C(NMe)CPhCPhC‐(NR)}(CNR)] (18, 19). Similar compounds 20–23 containing a five‐membered RhC4 metallacycle were prepared either from [C5H5Rh(RCCR′)(SbiPr3)] (7, 8) or [C5H5Rh‐(PhCCPh)(CNtBu)] (14) and excess isocyanide. The crystal and molecular structures of 17 and 18 (R = Me) have been determined.